Radiator plate and process for manufacturing the same

ABSTRACT

A radiator plate includes a metallic matrix and a dispersant. The metallic matrix exhibits a predetermined coefficient of thermal expansion. The dispersant is dispersed in the metallic matrix, and exhibits a coefficient of thermal expansion being smaller than that of the metallic matrix. The radiator plate has a heat-receiving surface, on which an electric device serving as a heat generator is disposed, and a heat-radiating surface for radiating heat received from the heat-receiving surface. The dispersant is dispersed more on the heat-receiving-surface side than on the heat-radiating-surface side. Thus, the radiator plate is inhibited from warping, and is good in terms of the dimensional stability as a final product. Moreover, the thermal resistance is diminished between the heat-receiving surface and the heat-radiating surface. Accordingly, the heat-radiating ability of the radiator plate is secured. Also disclosed is a process for manufacturing the radiator plate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat radiator, which is usedto radiate heat being emitted from a power module, and the like, and aprocess for manufacturing the same. The power module is, for example,constituted by an electric element (or electric device), which serves asa heat generator.

[0003] 2. Description of the Related Art

[0004] A chip (e.g., silicon chip, etc.), a power module, or the like,is essential to control a variety of apparatuses. In the chip, there aredisposed electric elements with a high density on a semiconductorsubstrate. In a power module, there are disposed a large number ofchips.

[0005] However, semiconductor products should usually be used indetermined service temperature ranges. When they are used outside theranges, they cause malfunctions. Accordingly, it is necessary toappropriately radiate heat, which is emitted from silicon chips, and soon. In particular, the higher the integration degree of chips is, or themore the control electric current enlarges, the more it is necessary toenhance the cooling ability for chips.

[0006] Hence, it has been carried out conventionally to dispose aradiator plate on the lower surface of silicon chips, etc. For example,in Japanese Unexamined Patent Publication (KOKAI) No. 11-126,870, thereis disclosed a radiator plate, which comprises a metal-based compositematerial using a ceramics dispersant. Specifically speaking, theradiator plate comprises a metal-based composite material, in which asilicon carbide powder, serving as a ceramics dispersant, is dispersedin an aluminum alloy, serving as a matrix. The aluminum alloy, whichexhibits a good heat transfer coefficient, is used as a matrix to securea heat-radiating ability. The silicon carbide, which exhibits a smallthermal expansion coefficient, is dispersed in the aluminum alloy toinhibit the radiator plate from warping. Note that fins are disposed onthe heat-radiating-surface side of the radiator plate, and that they aremanufactured by using a core, which is made from a readily-soluble salt(e.g., NaCl).

[0007] However, the radiator plate, set forth in the aforementionedpublication, is formed as a uniform organizational (or compositional)construction as a whole from the heat-receiving surface, on whichsilicon chips, or the like, exist, to the heat-radiating surface, onwhich the fins exist. Consequently, because of the temperature gradient,which arises from the heat-receiving surface to the heat-radiatingsurface, a gradient also takes place in the thermal expansion of theradiator plate. Namely, the thermal expansion is large on theheat-receiving-surface side, and it is small on theheat-radiating-surface side. Thus, warpage takes place in the entireradiator plate. Therefore, on the heat-receiving-surface side of theradiator plate, there might arise the fears of coming-off of the siliconchips, etc., therefrom, the degradation of contacting ability and thedeterioration of heat-radiating ability.

[0008] Further, since the silicon carbide is dispersed uniformly in theentire radiator plate, the thermal resistance enlarges to lower the heattransfer coefficient. Thus, the heat-radiating ability might beimpaired.

[0009] Furthermore, the conventional radiator plate is manufactured byusing the salt core. Note that, however, the salt core exhibits athermal expansion coefficient of about 46×10⁻⁶/K and the metal-basedcomposite material exhibits a thermal expansion coefficient of about8×10⁻⁶/K. Accordingly, there might arise a large thermal expansiondifference between them before and after the molten metal is solidified.Consequently, warpage might take place in the resulting radiator plateafter the casting. Hence, the dimensions of the final product might notbe stabilized.

[0010] Moreover, the salt core is manufactured for each of the radiatorplates. In addition, it is necessary to wash away the salt core withwater after casting the radiator plate. Hence, it is not possible to saythat the manufacturing process, set forth in the aforementionedpublication, is a preferable manufacturing process in terms of theman-hour requirement as well as the cost.

SUMMARY OF THE INVENTION

[0011] The present invention has been developed in view of thesecircumstances. It is therefore an object of the present invention toprovide a radiator plate, which is good in terms of the heat-radiatingability, and which can inhibit the warpage adequately.

[0012] Moreover, it is another object of the present invention toprovide a process for manufacturing such a radiator plate efficiently.

[0013] The inventors of the present invention researched earnestly tosolve the problems, made trial and error to achieve the objects, andcarried out a variety of systematic experiments repeatedly. As a result,they thought of dispersing a dispersant more on a heat-receiving-surfaceside of a radiator plate than on a heat-radiating-surface side thereof.Thus, they have completed the development of a radiator plate accordingto the present invention. At the same time, they have completed thedevelopment of a suitable process for manufacturing the present radiatorplate.

[0014] (Radiator Plate)

[0015] A radiator plate according to the present invention can carry outthe aforementioned object, and is characterized in that it comprises ametallic matrix exhibiting a predetermined coefficient of thermalexpansion, and a dispersant being dispersed in the metallic matrix andexhibiting a coefficient of thermal expansion being smaller than that ofthe metallic matrix; that the radiator plate has a heat-receivingsurface, on which an electric device serving as a heat generator isdisposed, and a heat-radiating surface for radiating heat received fromthe heat-receiving surface; and that the dispersant is dispersed more ona side of the heat-receiving surface than on a side of theheat-radiating surface.

[0016] Since the dispersant of smaller thermal expansion coefficient isdispersed more on the side of the heat-receiving surface, in which anelectric device serving as a heat generator is disposed, the thermalexpansion is controlled on the heat-receiving-surface side. Accordingly,it is possible to secure the bonding ability or adhesion ability withrespect to silicon chips, etc. Moreover, even when there arises atemperature gradient from the heat-receiving-surface side to theheat-radiating-surface side, it is possible to control or inhibit thewarpage of the entire radiator plate because the dispersant of smallerthermal expansion coefficient is distributed more on theheat-receiving-surface side.

[0017] Moreover, contrary to a case where a member of small thermalcoefficient is cast into a metal, in the heat radiator plate accordingto the present invention, it is possible to make the thermal resistanceless and to inhibit a boundary layer from forming abruptly, because thedispersant of small thermal expansion coefficient is suitablydistributed gradiently.

[0018] In particular, it is appropriate that, in the radiator plateaccording to the present invention, the metallic matrix can comprisealuminum as a major component and the dispersant can comprise a primarycrystal including silicon as a major component.

[0019] The primary crystal (i.e., dispersant) comprising silicon as amajor component exhibits a thermal expansion coefficient, which is inthe proximity of a thermal expansion coefficient exhibited by asubstrate made from silicon. Consequently, the thermal expansiondifference can be furthermore diminished between the dispersant and thesubstrate. In addition, it is possible to readily produce the primarycrystal comprising silicon as a major component, not by separatelyadding the dispersant to a molten alloy, but by controlling asolidifying temperature of the molten alloy. In addition, when themetallic matrix comprises aluminum as a major component, it is possibleto obtain a radiator plate, which is good in terms of the thermaltransfer ability and heat-radiating ability.

[0020] (Process for Manufacturing Radiator Plate)

[0021] A process for producing a radiator plate according to the presentinvention can carry out the aforementioned object, and is characterizedin that it comprises the steps of: pressurizing and charging ahypereutectic molten alloy into a cavity of a mold with a filteringmember disposed therein, the filtering member having opposite sides,from one of the opposite sides of the filtering member at a temperatureof generating a primary crystal or less; and solidifying the resultingmolten alloy after accumulating the primary crystal, being generated inthe pressurizing-and-charging step, on the one of the opposite sides ofthe filtering member.

[0022] By maintaining the hypereutectic molten alloy at an appropriatetemperature, the hypereutectic component arises as a primary crystal.Then, the primary crystal, which arises in the cavity of the mold, isfiltered out by the filtering member in the pressurizing-and-chargingstep, and is accumulated on the one of the opposite sides of thefiltering member. Under the circumstance, when the resulting moltenalloy is cooled by cooling the mold or by the other methods (i.e., thesolidifying step), it is possible to obtain a radiator plate, in whichthe primary crystal is accumulated on the one of the opposite sides ofthe filtering member.

[0023] Moreover, it is appropriate that the hypereutectic molten alloycan be an aluminum-silicon molten alloy whose hypereutectic component issilicon.

[0024] Thus, it is possible to efficiently manufacture theaforementioned radiator plate. Note that the resulting radiator plate isconstituted by the metallic matrix, which comprises aluminum as a majorcomponent, and the dispersant, which comprises a primary crystalincluding silicon as a major component.

[0025] In addition, in a case where the hypereutectic molten alloy ispressurized and charged from the heat-radiating-surface side withrespect to the filtering member (see FIG. 1.), it is appropriate thatthe present production process can further comprise the step of removingthe filtering member after the solidifying step.

[0026] Note that the filtering member, which comprises a formedsubstance, or the like, made, for example, from ceramic fibers, canremain on the resultant heat radiator plate. However, when the filteringmember is removed, it is possible to obtain the heat radiator plate,which warps less, and which is good in terms of the heat-radiatingability.

[0027] In accordance with the radiator plate according to the presentinvention, since the dispersant of small thermal expansion coefficientis present more on the heat-receiving-surface side, it is possible todiminish the thermal resistance between the heat-receiving surface andthe heat-radiating surface. Accordingly, it is possible for the presentradiator plate to secure the heat-radiating ability. Moreover, thepresent radiator plate is inhibited from warping, and is good in termsof the dimensional stability as a final product.

[0028] In accordance with the process for manufacturing a radiatorplate, it is possible to manufacture such a good radiator plate not onlywith a good productivity but also at a less expensive cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] A more complete appreciation of the present invention and many ofits advantages will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings and detailedspecification, all of which forms a part of the disclosure:

[0030]FIG. 1 is a schematic diagram for illustrating a process formanufacturing a radiator plate, an example according to the presentinvention;

[0031]FIG. 2 is a cross-sectional side view for illustrating a radiatorplate, an example according to the present invention; and

[0032]FIG. 3 is a schematic diagram for illustrating a process formanufacturing a radiator plate, another example according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Having generally described the present invention, a furtherunderstanding can be obtained by reference to the specific preferredembodiments which are provided herein for the purpose of illustrationonly and not intended to limit the scope of the appended claims.

[0034] The present invention will be hereinafter described in detailwith reference to specific examples of the radiator plate andmanufacturing process according to the present invention.

[0035] (1) Metallic Matrix

[0036] In addition to aluminum, the metallic matrix can be pure metalsand a variety of alloys thereof. For example, the pure metals can bemagnesium, copper, zinc, and the like.

[0037] (2) Dispersant

[0038] The dispersant can be such a material that can control thethermal expansion on the heat-receiving-side of the radiator plate.Accordingly, the dispersant can comprise a variety of ceramic fibers.However, as set forth above, the dispersant can preferably be composedof primary crystal silicon particles in view of the thermal expansioncoefficient, thermal resistance, and so on. Moreover, the primarycrystal silicon particles can comprise a silicon simple substance, orcan be compounds, and the like, which are composed of the metallicmatrix (e.g., aluminum, alloy components, etc.) and silicon.

[0039] (3) Filtering Member

[0040] The filtering member accumulates the primary crystal thereon butpasses the other molten alloy therethrough. Consequently, depending onthe sizes of the primary crystal to be accumulated, the filtering membercan be selected from a variety of filtering members having a desiredpore diameter.

[0041] Specifically, the filtering member is a member, which is formedso as to conform to a configuration of a cavity in a mold by usingfibers, whiskers, or the like, being composed of silicon carbide,carbon, alumina, alumina-silica, glass, and so on. Further, thefiltering member can preferably have such a strength that it does notdisintegrate when the hypereutectic molten alloy is pressurized andcharged into the cavity. Furthermore, the filtering member canpreferably be such a material that it hardly reacts with thehypereutectic molten alloy, or that it hardly forms new compounds withthe hypereutectic molten alloy. Therefore, the filtering member can beselected while taking the compatibility with the hypereutectic moltenalloy into consideration. For instance, in a case where thehypereutectic molten alloy is an aluminum-silicon alloy whosehypereutectic component is silicon, it is preferable to use a filteringmember, which is made from alumina-silica.

[0042] (4) Others

[0043] When the present radiator plate is provided with a fin, or thelike, on the heat-radiating surface, it is possible to achieve theenlargement of the heat-radiating area so that the present radiatorplate can be enhanced in terms of the heat-radiating ability. Further,it is not necessary to cast the present radiator plate for each of finalproducts. The present radiator plate can be cast for a plurality offinal products at once. Then, the present radiator plate can be cut anddivided to a size of the respective final products.

[0044] Furthermore, when the hypereutectic molten alloy is pressurizedin the pressurizing-and-charging step, the hypereutectic molten alloycan be pressurized to such a magnitude that the hypereutectic moltenalloy impregnates into and penetrates through the filtering member.Thus, it is possible to employ an injection molding process, a diecasting process, and so on. Moreover, the temperature of thehypereutectic molten alloy can be adjusted by heating or thermallyinsulating a plunger, a mold, or the like.

EXAMPLES

[0045] The present invention will be hereinafter described morespecifically with reference to examples of the radiator plate andmanufacturing process therefor according to the present invention.

[0046] (Radiator Plate)

[0047] A radiator plate 10, one of the examples according to presentinvention, is illustrated in FIG. 1.

[0048] The radiator plate 10 comprises a heat-radiating portion 11 and aheat-receiving portion 12. The heat-radiating portion 11 has short fins,which are disposed on the heat-radiating side. The heat-receivingportion 12 is disposed on the heat-receiving side. It is manufacturedfrom a molten aluminum (Al)-silicon (Si) alloy by a manufacturingprocess described later. For example, the molten Al—Si alloy is the A390alloy, whose silicon content is 17% by mass, as per the standard of theASTM (American Society for Testing and Materials).

[0049] The heat-receiving portion 12 has an accumulated Si layer 13, inwhich silicon primary particles are accumulated primarily. For instance,the accumulated Si layer 13 included Si in an amount of 30% by mass inthe outermost surface when the entirety was taken as 100% by mass. TheSi content changed gradually to that of the Al—Si alloy matrix, whichincluded Si in an amount of 17% by mass approximately, from theuppermost surface to the lowermost surface (i.e., from theheat-receiving surface to the heat-radiating surface) in this order.

[0050] (Manufacturing Process for Radiator Plate)

[0051] Hereinafter, a process for manufacturing the radiator plate 10will be described with reference to FIG. 1. FIG. 1 schematicallyillustrates an outline of a die casting machine 100, which was used tomanufacture the radiator plate 10. FIG. 2 illustrates the resultingradiator plate 10.

[0052] The die casting machine 100 was equipped with an upper die (notshown) and a lower die 110, two of which served a die as a whole. In acavity of the die, a filtering member 120 was disposed which conformedto a configuration of the cavity. Note that the filtering member 120 wasproduced by pressurizing and molding whiskers, which were made fromalumina-silica.

[0053] Thereafter, the aforementioned molten Al—Si alloy was pressurizedand charged by a plunger from the side of the lower die 110 (i.e., thepressurizing-and-charging step). At this moment, the temperature of thelower die 110 was adjusted to and maintained at such a temperature thatthe Si primary crystal particles arose in the molten Al—Si alloy.

[0054] Moreover, in the pressurizing-and-charging step, the chargingpressure was controlled to such a pressure that the molten Al—Si alloy,which was free from the primary crystal particles having a predeterminedparticle diameter or more, penetrated through the filtering member 120without destroying the filtering member 120. For instance, the chargingpressure fell in a range from dozens of MPa to 100 MPa.

[0055] Then, while leaving the filtering member 120 in the cavity, thedie was cooled, thereby solidifying the molten Al—Si alloy (i.e., thesolidifying step). After detaching the molded product from the die, thefiltering member 120 was removed by machining (i.e., the removing step).Note that, at this moment, it is possible to efficiently manufacture theradiator plate 10 by carrying out finishing the heat-receiving surfaceof the radiator plate 10, simultaneously with carrying out the removingstep.

[0056] (Others)

[0057]FIG. 3 illustrates another process for manufacturing a radiatorplate 20 according to the present invention. Note that, in a die castingmachine 200 illustrated in FIG. 3, a pouring direction of a molten Al—Sialloy differs from that of the above-described example. Namely, themolten Al—Si alloy was pressurized and charged from theheat-receiving-surface side of the radiator plate 20 (i.e., from theside of a not-shown upper die), thereby forming an accumulated Si layer13′ on an upper-surface side of a filtering member 220. In this case, itwas not necessary to remove the filtering member 220, because theaccumulated Si layer 13′ had been already formed on theheat-receiving-surface side. Note that, in order to secure a flatness ofthe heat-receiving surface, the finish processing can be carried outonto the accumulated Si layer 13′.

[0058] Moreover, since Si primary particles, which had a predeterminedparticle diameter or more (e.g., from 20 to 100 μm), were filtered out,the heat-radiating portion of the radiator plate 20 comprised an Al—Sialloy, from which the Si primary crystal particles having apredetermined particle diameter or more were removed. Moreover, theSi—Al alloy was fine and uniform, and included Si primary crystalparticles, which had passed through the filtering member 220 and whichhad a particle diameter of a couple of μm or less.

[0059] The thus obtained radiator plates 20 were warped less, and weregood in terms of the dimensional stability as a final product. Further,they were good in terms of the heat radiating ability. Furthermore, byemploying the manufacturing process according to the present invention,such radiator plates could be manufactured with ease as well as with ahigh productivity.

[0060] In the above-described examples, the radiator plates wereexemplified in which the fins existed on the heat-radiating-surfaceside. Note that, however, it is needless to say that the presentinvention can be applied to a simple plate-shaped radiator, which isfree from the fins.

[0061] Such a plate-shaped radiator can be used in a case, for example,where heat is released by adhering a heat-radiating surface of a powermodule onto a heat sink or a box of instruments, and so on.

[0062] Having now fully described the present invention, it will beapparent to one of ordinary skill in the art that many changes andmodifications can be made thereto without departing from the spirit orscope of the present invention as set forth herein including theappended claims.

What is claimed is:
 1. A radiator plate, comprising: a metallic matrixexhibiting a predetermined coefficient of thermal expansion; and adispersant being dispersed in said metallic matrix and exhibiting acoefficient of thermal expansion being smaller than that of saidmetallic matrix; said radiator plate having a heat-receiving surface, onwhich an electric device serving as a heat generator is disposed, and aheat-radiating surface for radiating heat received from theheat-receiving surface; said dispersant being dispersed more on a sideof said heat-receiving surface than on a side of said heat-radiatingsurface.
 2. The radiator plate according to claim 1, wherein: saidmetallic matrix comprises aluminum as a major component; and saiddispersant comprises a primary crystal including silicon as a majorcomponent.
 3. The radiator plate according to claim 1, wherein saidmetallic matrix is at least one member selected from the groupconsisting of pure metals and alloys thereof.
 4. The radiator plateaccording to claim 3, wherein the pure metal is at least one memberselected from the group consisting of aluminum, magnesium, copper andzinc.
 5. The radiator plate according to claim 1, wherein saiddispersant is composed of primary crystal silicon particles.
 6. Theradiator plate according to claim 5, wherein said primary crystalsilicon particles comprise at least one member selected from the groupconsisting of a silicon simple substance and compounds being composed ofsaid metallic matrix and silicon.
 7. A process for manufacturing aradiator plate, comprising the steps of: pressurizing and charging ahypereutectic molten alloy into a cavity of a mold with a filteringmember disposed therein, the filtering member having opposite sides,from one of the opposite sides of the filtering member at a temperatureof generating a primary crystal or less; and solidifying the resultingmolten alloy after accumulating the primary crystal, being generated insaid pressurizing-and-charging step, on said one of the opposite sidesof the filtering member.
 8. The process for manufacturing a radiatorplate according to claim 7, wherein said hypereutectic molten alloy is amolten aluminum-silicon alloy whose hypereutectic component is silicon.9. The process for manufacturing a radiator plate according to claim 7,after said solidifying step, further comprising the step of removingsaid filtering member.
 10. The process for manufacturing a radiatorplate according to claim 7, wherein the filtering member is made from atleast one member selected from the group consisting of fibers andwhiskers.
 11. The process for manufacturing a radiator plate accordingto claim 10, wherein the fibers and whiskers are composed of at leastone member selected from the group consisting of silicon carbide, carbonalumina, alumina-silica and glass.
 12. The process for manufacturing aradiator plate according to claim 7, wherein the filtering member hardlyreacts with said hypereutectic molten alloy or hardly forms newcompounds with said hypereutectic molten alloy.